This is a photo taken of fireflies in the rain clinging onto leaves of a tree outside my window.

The following is a description of fireflies in the Wikipedia:

Lampyridae is a family of insects in the beetle order Coleoptera. They are winged beetles, and commonly called fireflies or lightning bugs for their conspicuous crepuscular use of bioluminescene to attract mates or prey. Fireflies produce a “cold light”, with no infrared or ultraviolet frequencies. This chemically produced light from the lower abdomen may be yellow, green, or pale red, with wavelengths from 510 to 670 nanometers.

Zooming out, you can see more of the tree – it is almost like a Christmas tree with fireflies clinging onto.

Under rain, understand fireflies wouldn’t fly but cling on to trees. But why do they hang on to this tree?

I was not able to improve on the picture as the tree swayed in the rain, increasing the exposure would not improve the contrast between the fireflies and the surrounding!